1. Field Of Invention
This invention relates to a chain and sprocket combination that reduces wear and allows for an increase in the speed of operation of the devices that use chain and sprockets.
2. Description Of Prior Art
Three basic problems exist when a chain engages a sprocket. First, because a chain hinges freely, the rise and fall of the chain relative to a sprocket as it enters and exits the sprocket goes unrestrained. This rise and fall results from a phenomena known as chordal action. (Reference ACME Chain, p. 102.) The unrestrained fall results in the chain's links striking the sprocket with an impact velocity. Therefore, the unrestrained hinging allows the links to act like a hammer causing a detrimental pounding of the chain against the sprocket. Second, engagement of the sprocket teeth with the chain results in a sliding of the chain across the teeth of the sprocket. This sliding motion occurs mainly because the chain is not fully seated on the sprocket when engagement occurs. Third, as a chain hinges about a sprocket sliding friction is produced between the pins and bushings of the chain's hinge joints. These three problems result in slower allowable chain speeds in order to reduce wear and increase durability. Furthermore, all of these problems are magnified as chain size is increased, when lubrication is inadequate, and for abrasive working environments.
U.S. Pat. No. 4,116,497 teaches that a tractor which has caterpillar type track can be made to operate with less noise by equipping the track's hinge joints with an external spring located off to the side of the track. The spring stores some of the energy which is normally lost due to chordal action thus reducing noise. This invention deals specifically with track art and does not clearly teach its use for which there is a separate art classification. Also, this invention does not clearly teach how to eliminate chordal action but rather how to reduce noise which is merely a side effect of chordal action. Furthermore, the embodiments of this invention are so large and heavy that they would not be practical for chain and sprocket applications where, unlike tracked vehicles, large chain size and weight are undesirable.
U.S. Pat. No. 1,958,139 and many others teach the use of an elastomer bushed chain, wherein hinging of the chain takes place by deformation of the elastomer material. This eliminates sliding friction between the pins and bushings of a chain. This also eliminates the need for lubrication. It also allows for operation in abrasive environments without pin and bushing wear. This invention along with the many others dealing with elastomer bushed chains all focus on the elastomer bushings ability to eliminate wear, dampen vibrations, and reduce noise. However, none teach that the detrimental pounding of a chain onto a sprocket caused by chordal action can be reduced or eliminated by using the torsional spring characteristics of the elastomer bushing.
My U.S. Pat. No. 4,671,783 and others teach that a sprocket with a plurality of cam actuated teeth that engage a chain after it is seated on the sprocket will eliminate the sliding of the chain across the teeth. This eliminates the need for lubrication and allows for the chain and sprocket to operate with greatly reduced wear in abrasive environments.